The present invention relates generally to power transfer devices for applying backup electrical power to electrical systems having an internal direct current (DC) bus, and more specifically to a simultaneous power supply source (SPSS) power transfer device for applying backup electrical power to such electrical systems.
Critical electrical equipment in shipboard systems and in other systems must have uninterrupted power and thus is supplied from either a primary power source or a back-up power source upon failure of the primary power source. The transfer between electrical power sources is accomplished by the use of bus power transfer devices. If the normal power source in use fails, the bus power transfer device will accomplish a transfer of electrical power from the normal source to an alternate source of power to ensure that system equipment will continue to receive operating power. There are two types of prior art bus power transfer devices, the automatic bus transfer (ABT) device and the manual bus transfer (MBT) device. The ABT will transfer automatically, while the MBT requires human intervention to accomplish the power transfer.
Prior art ABT devices exhibit power transfer time delays which cause problems when switching to backup power for computers and other sensitive electrical equipment. The problem typically comes about because the time delay before switchover is complete represents an interval of either no power or unacceptable power conditions, during which the protected equipment is in an indeterminate operational condition. This typically means that data may be lost due to degraded power conditions internal to the protected electrical equipment. Additionally, when system power is reapplied after this no-power interval the protected equipment may not be properly configured for a turn-on condition. There are therefore two problems associated with prior art ABT devices: the transfer delay time which results in momentary power loss or unacceptable degradation and the reapplication of power when the protected equipment is in an unknown startup configuration.
Because of these problems with prior art ABT devices, MBT devices may be utilized. The MBT devices are slow because they are manually operated. This is a problem in many applications, but until the present invention the ABT prior art problems have not been successfully resolved. The need for MBT devices comes about because a power interruption can occur during the transfer of the ABT device itself, which places the protected equipment in an unknown startup configurations; if the MBT device is utilized the reapplication of power may be applied properly (but slowly). As a result of prior art power transfer device limitations, prior art power backup transfer systems have the inherent problems described.
Currently there is no known prior art transfer device available that will keep voltage sensitive types of protected equipment on-line operating correctly during power interruptions except for an electronic bus transfer (EBT) device that is projected to be large, complex, heavy and costly, and has not been proven in a shipboard environment. Such an EBT device requires sophisticated electronics which have high maintainability costs and lower reliability in order to accomplish transfer between asynchronous power sources.
There is thus an unmet need in the art to be able to provide the transfer to backup electrical power without the disadvantage of a transfer time delay which would result in a momentary power interruption or momentary degradation which in turn could produce loss of data or unknown equipment configurations. Therefore, it would be advantageous in the art to be able to provide the aforementioned power transfer using a power transfer device which is simple, inexpensive, and will operate automatically while solving the aforementioned problems.